1. Field of the Invention
The present invention generally relates to an optical system for the delivery of a collimated beam of light in conjunction with an industrial manipulator. More particularly, the invention provides a two axis optical wrist for use in combination with a robotic laser beam delivery apparatus.
2. Description of the Prior Art
High powered lasers are ideally suited for use as a source of heat in various metal processing applications which include the vaporization of materials, such as in drilling and cutting operations. Lasers are also applicable to procedures, such as, welding or surface cladding of materials, which require the melting of materials. Also, the temperature of solid phase materials can be varied, by use of the laser in hardening and annealing operations.
The thermal effects which are experienced by materials when exposed to the laser beam are primarily dependent on the intensity of laser energy, the absorptivity and reflectivity of the material and the length of time during which the material is exposed to the laser beam. Precise control over these parameters determines the resulting change in the phase or the state of the material. Usually, when lasers are employed in processes such as welding, cutting and surface treatment, the area of the workpiece to be processed is oriented in such a way that it is nearly normal to the laser beam with the beam impinging squarely on its surface. This configuration optimizes the absorptivity of the material and facilitates its heating. Generally, the laser and the workpiece are cause to move relative to each other. This relative motion can be accomplished in two ways. First, the beam can be traversed over a stationary workpiece. Second, the workpiece can be manipulated under a fixed laser beam. The former method requires that the laser beam be moved either by mounting the laser on a movable device or by directing the beam from a fixed laser to the workpiece through the use of a movable optical system. The latter method requires the use of a workpiece manipulating device.
Generally, the latter method is employed. Most present systems which use the laser for material processing employ a fixed laser beam along with the apparatus that is capable of manipulating the workpiece. This manipulation of the workpiece usually incorporates linear or rotational movement of the part and exploitation of the part's symmetry. Symmetrical or simple parts can be processed by machines having one or two axes of freedom, but any moderately complex workpiece requires a part manipulating apparatus which has the capability of providing four or five degrees of freedom. The required manipulations of such workpieces, along with the general requirement that the laser beam impinge the work surface normally, are difficult to achieve with currently available part handling devices. Furthermore, these devices are usually made for specific parts and have dedicated hardware. Therefore, they are not readily retooled when changes in part shape and dimension occur. Other disadvantages of this type of equipment are that large, cumbersome parts are difficult to position accurately and repeatedly and have significant inertial effects when moved. Also, due to part geometry, obstructions may occur which prevent a clear "line of sight" between the laser beam source and the working surface of the workpiece.
A significant contribution to the resolution of the aforedescribed problem has been contributed by Daniel J. Plankenhorn in U.S. Pat. No. 4,539,462, entitled "Robotic Laser Beam Delivery Apparatus". This patent is assigned to the assignee of the present invention and incorporated herein by reference as it fully set forth. In this patent, a light beam directing apparatus is described which permits a reflected beam of light such as a laser, to be directed in a path which comprises a plurality of straight segments. Each segment of the beam is associated with a segment of the robot's arm in a fixed spatial relationship. The laser beam delivery system provides optical joints which are used in conjunction with an industrial manipulator so that the axes of motion of both are synchronous and incapable of mutual interference.
The laser beam delivery system is ideally suited for use with a general purpose orthogonal axis manipulator system which is taught in U.S. Pat. No. 4,571,149 to Soroka et al. This patent teaches an orthogonal axis manipulator system which is commercially available as the Unimate 6000 Series from Westinghouse Electric Corporation. This patent is also incorporated herein by reference as if fully set forth. By definition and solid analytic geometry, in a rectangular-coordinant system, all points in space can be reached at any rectangular orientation through six degrees of freedom. These six degrees consist of three translations usually referred to as X, Y, and Z axes and three rotation .theta..sub.X, .theta..sub.Y, and .theta..sub.Z. Many machine tools and robots use only five degrees of freedom with the sixth degree, .theta..sub.Z, eliminated since its motion is end effector rotation about itself and would be better accomplished by other mechanical designs such as a spindle.
As should be evident from the earlier discussion, these five degrees of freedom or motion are thus also what is required in an industrial material processing laser system in order to move the beam to do useful work. Obviously, depending upon the robot's geometry, there are a variety of reproaches to fitting the required laser beam optics to a given industrial manipulator.
A variety of optical wrists or optical head configurations have been suggested in the literature to provide the necessary degrees of freedom for useful laserrobotic applications. An example of which can be found in the Plankenhorn patent identified above in which optical joints comprise tubular members and are rotatably connected to each other but are not necessarily automatically driven in a relative rotational direction during the operation of the robot. A similar optical head or wrist is shown in U.K. Patent Application No. 2,131,388A to David et al. Attempts have been made to motorize such optical wrists or optical focussing devices and an example of this is found in U.S. Pat. No. 3,986,767 to Rexer et al. entitled "Optical Focus Device". This patent teaches an apparatus for focussing a beam of collimated radiation by the use of a focus head having an off-axis parabolic section in combination with a flat turning mirror. The head is capable of rotating the beam about two orthogonal axes and is mounted in a gantry which permits three-dimensional movement of the entire head. The rotation of the head is effected by means of a gear train and drive motor associated with each degree of freedom. The use of such a system to effect the movement of the optical head provides the obvious problem of gear backlash as well as the inaccuracies consistent with such a structure. The use of a hollow shaft motor has been suggested in U.S. Pat. No. 4,413,180 for a device used in image acquisition. The motor itself in such a system drives an optical beam appointing and spreading assembly comprising a fixed cylindrical reflector having a concave, light reflecting inner surface.
It is an object of this invention to provide a simplified optical wrist for use with laser beam delivery equipment.
It is also an object of this invention to provide an optical wrist for laser applications in which the laser beam lies on the central line of the rotational axes of the optical wrist.
It is still another object of this invention to provide in combination with an industrial manipulator having a laser beam delivery system integral therewith, a two-axis optical wrist for laser applications.